Minimal traumatic brain injury causes persistent changes in DNA methylation at BDNF gene promoters in rat amygdala: A possible role in anxiety-like behaviors

Abstract

Minimal traumatic brain injury (MTBI) often transforms into chronic neuropsychiatric conditions including anxiety, the underlying mechanisms of which are largely unknown. In the present study, we employed the closed-head injury paradigm to induce MTBI in rats and examined whether DNA methylation can explain long-term changes in the expression of the brain-derived neurotrophic factor (BDNF) in the amygdala as well as trauma-induced anxiety-like behaviors. The MTBI caused anxiety-like behaviors and altered the expression of DNA methyltransferase (DNMT) isoforms (DNMT1, DNMT3a, and DNMT3b) and factors involved in DNA demethylation such as the growth arrest and DNA damage 45 (GADD45a and GADD45b). After 30days of MTBI, the over-expression of DNMT3a and DNMT3b corresponded to heightened DNMT activity, whereas the mRNA levels of GADD45a and GADD45b were declined. The methylated cytosine levels at the BDNF promoters (Ip, IVp and IXp) were increased in the amygdala of the trauma-induced animals; these coincided negatively with the mRNA levels of exon IV and IXa, but not of exon I. Interestingly, treatment with 5-azacytidine, a pan DNMT inhibitor, normalized the MTBI-induced DNMT activity and DNA hypermethylation at exon IVp and IXp. Furthermore, 5-azacytidine also corrected the deficits in the expression of exons IV and IXa and reduced the anxiety-like behaviors. These results suggest that the DNMT-mediated DNA methylation at the BDNF IVp and IXp might be involved in the regulation of BDNF gene expression in the amygdala. Further, it could also be related to MTBI-induced anxiety-like behaviors via the regulation of synaptic plasticity.